Conversion of diborane



United W Pate t This invention relates to the conversion of diborane to higher boron hydrides. More particularly it relates to the conversion of diborane'to higher boron hydrides employing gamma radiation.

The higher boron hydrides such as tetraborane and p'entaborane are usefulias welding fuels, as described in US. Patent 8,582,268, and for other-purposes.

--.'.*It' has now been found that tetraborane and other higher boron hydrides can be obtained by subjecting diborane to gamma radiation. present invention, diborane at a temperature of about 0 to 40 C. is subjected to a source of gamma radiation of suitable intensity and for suflicient time to provide a total radiation of about 1 to 50 million roentgens. A total radiation of less than about one million roentgens at temperatures in the vicinity of 0 C. provides little conversion while higher total radiations at higher temperatures provides conversions-of diborane to higher boron hydrides of ,4 to 6% or even higher.

"Anysmt'able source of amma radiation can be used Thus according to the in the process of this invention. Cobalt-60 is a particularly convenient source of suitable intensity and is readily available'by'the radiation of ordinary cobalt in an atomic reactor. Tantalum-182 is another suitable gamma radiation source. Mixed elements from an atomic reactor, designated as hot fuel elements," containing various radioactive isotopes formed when either uranium or plutonium undergo fission, can be'used. The fission products can be used as such or may be partially or completely separated into radioisotopes. Direct gamma radiation, which can be mixed with neutrons, is also useful for the purposes of the present invention. The presence of beta rays in the gamma rays does not apear to be deleterious although the beta radiation appears to be inactive in effecting chemical conversions because of its low penetration.

The cobalt-60 source of gamma radiation is particularly convenient and accessible. It has a half life of about 5.1 years and the hard gamma radiation therefrom oomprises rays of 1.17 mev. (mill-ielectron volts) and 1.34 mev. in cascade. The cobalt-60 source can be in any suitable form and arranged in any desired manner. For example, it can comprise pellets about 1 centimeter in diameter by 1 centimeter in length embedded in the end of a steel or lead piston. Alternatively, the cobalt-60 source can be in cylindrical form. In use the radiation source is provided with suitable shields for the protection of personnel which still allow irradiation of the sample. Lead is a particularly suitable shield material and a thickness of 8 to 10 inches in all directions from the radiation source appears to be sufiicient to provide adequate protection.

The cobalt-60 source can vary in intensity, for example, it can be 300 or 400 curie material. Cobalt sources of greater or lesser intensity can be used and the time of exposure adjusted accordingly to provide adequate dosage.

Where desired, gaseous diluents may be used with the primary reactants. For this purpose, argon or helium are preferred, although nitrogen or hydrogen may be used.

The use of somewhat elevated pressures is usually desir- 3,001,920 I Patented Sept. 26, 1061 ICE 2 able for the most advantageous results although, for some purposes, the use of atmospheric or subatmospheric pressures may be desirable. The use of about 2fto'20 atmospheres pressure is particularly'advantageous. The sample of the material to be treated is contained in a stainless steel or other suitable metallic reactor. It may be desirable, particularly where solid or liquid products are formed, to use a glass or other suitable liner for such metallic containers. The design and material of the container will depend in large part on the pressure to be used or developed during the irradiation.

'No significant temperature effect occurs during the it:- radiation and usually the large bulk of shielding mate'- rial serves to maintain the reaction mixture at substan; tially constant temperature. Where desired, suitable means of heating or refrigeration can be arranged "to maintain constant temperature conditions. I The irradiation can beca'rried out at reduced or elevated temperatures, for example, from -40 C. to C. or more.

In'the following examples, a cobalt-60 radiation source which had a strength of approximately 400 curies was It consisted of a hollow cylinder approximately 13% inches in length by 2.3 inches outside diameter and 1.7 inches inside diameter. The cobalt was encased in' a stainless steel shell and surrounded by cooling coils packed in thermal insulating material. The whole assembly had a diameter of approximately 5 inches and was placed in a lead pig. The pig was a cylinder with a central core Sinches in diameterand a wall thickness of 8 inches. The lead pig also had a base 8 inches thick below the cobalt cylinder. The upper portion of the lead pig serv} ing as a lid consisted of three inches of lead and 7 inches of steel. Using this source and geometry of equipment, the average dose in the irradiation region was 150,000 roen'tg'en's per hour (one roentgen is equivalent to. 9'3 ergs per gram).

Example I A'stainless steel bottle about 1.5 inches in diameter and 12 inches in length having a capacity of ml. and fitted with suit-able valve inlets was thoroughly washed with detergents and water, rinsed thoroughly with water and evacuated while heating to 60-80 C. The clean, dry cylinder was connected to a vacuum manifold and evacuated to a few microns pressure. The evacuated system was checked for leaks by standing for several hours and observing the pressure. If the system was not tight the above procedure was repeated. When the system was tight, diborane was introduced into the manifold and condensed into the irradiation cylinder by maintaining the latter at liquid nitrogen temperature. The valves on the irradiation cylinder were closed and the bomb removed trom the manifold and transferred to the irradiation chamber described above.

The charge was 78.4 mi-llimoles of diborane.

At atmospheric temperature, the pressure was about ten atmospheres.

The bottle containing the diborane was introduced into the irradiation assembly and exposed to gamma radiation at a dosage rate of 150,000 roentgens per hour for 24 hours. This amounts to a total dosage of 3,600,000

roentgens. During the treatment the irradiation cylinder By fractional condensation .the tetraborane -can be recovered and unreacted diborane recycled for additional treatment.

Example .II

An irradiation cylinder cleaned as described in Example '1 was charged with 75.8 millimoles of 'diborane and irradiated as described "in Example I but at 25 C. tor 168 hours. The total exposure amounted to 25.2 million'roentgens. Infrared analysis of the product mixtureindicated that "it contained 95.1 percent of the boron "in'the form of diborane, 4.0 percentin the form of tetraborane, 0.83 percentin theform ofpentaboranefll) and :08 percent intheform of solids. This corresponds to *a conversion of about 4 percent of the charged diborane "to tetraborane.

'The 'products can be readily separated by fractional condensation and the unreacted diborane recycled for "further treatment.

Other useful interconversions of boron hydrides are effected according'to the present invention by irradiation with gammarays. For example, the method can also be 'applied'to the further irradiation of .tetraborane, the irradiation of pentaborane(9), pentaboranefll), decaborane, or of the yellow "solids produced'bypyrolysis of lower boron hydrides. Organic derivatives of the hypothetical'BH can be irradiated, for example, trimethylborane, 'triethylborane, triisobutylborane and higher .honrologues. To obtain useful products it is not necessary to useindividual compounds as starting materials, .for

example, mixtures of boron hydrides can be used. A mixture of dihorane and tetraborane is a suitable-startingmaterial aswell as mixtures of diborane with pentab'orane(9), pentaborane(1l), and trialkylboranes. Reactions "of boron hydrides with'other materials can also be'efiected using gamma radiation. Thus, a mixture of 'diborane with ethylene or other olefinic or acetylenic materials with various boron hydrides can be treated. Propylene, butene-l, 'butene-Z and Z-methylpropene-l or mixtures of such olefins with boron hydrides can be irradiated according to the process of the present invention. Acetylene, methylacetylene, allene, butadiene 1,3, 2-

. 4 .methylbutadieneelj ,and other unsaturates admixed with boron hydrides can be irradiated. In some cases hydrogen can additionally be introduced, particularly in the treatment of the yellow solids obtained by pyrolysis of lower boron hydrides. Thus mixtures of hydrogen and yellowsolids can be irradiated. Olefins or ;acetylenes f gr example, ethylene or acetylene itself can be incorporated in such mixtures and subjected to gamma radiation. Alkyl borohydri'des, for examples, ethyldecaborane or ethylpentaborane can be treated in admixture with diborane. The method is also useful for the hydrogenation of borate esters, .for example, trimethylborate, for the hydrogenation of mixtures of boron halides and alkali or alkaline earth metals, including magnesium, to form boron :hydrides and for the hydrogenation of metal boridesyfor example, .ferric boride or calcium hexaboride .or forthe hydrogenation of1boron carbides, for example, B C.

Weclaim:

1. .Aprocessv tor the conversion ofediborane-toa product mixture ,c ontain ing tetrahorane andother higher boron hydrides whichcomprises subjecting the diborane at a temperature of about .0" to 40 C. to -a-source of gamma radiation.of;suitable.intensity and for asufiicient timesto provide a totalnradiation .of about .1 to million roentgens.

.2. Theprocessofclaiml in-whichthe sourcenf: radiation is cobalt-.60.

References Cited in the'fileof this patent 

1. A PROCESS FOR THE CONVERSION OF DIBORANE TO A PRODDUCT MIXTURE CONTAINING TETRABORANE AND OTHER HIGHER BORON HYDRIDES WHICH COMPRISES SUBJECTING THE DIBORANE AT A TEMPERATURE OF ABOUT 0* TO 40*C. TO A SOURCE OF GAMMA RADIATION OF SUITABLE INTENSITY AND FOR A SUFFICIENT TIME TO PROVIDE A TOTAL RADIATION OF ABOUT 1 TO 50 MILLION ROENTGENS. 